Transpacific truck was travelling at 151kph at base of South Eastern Freeway, inquest told

A truck that crashed into three cars killing two people in Adelaide was travelling at an average speed of 151.9kph in the moments leading up to the crash, an inquest has heard.

The coronial probe began this morning into the deaths of Tom Spiess and Jacqui Byrne who were killed when the tanker owned by Transpacific crashed into the vehicles on Monday.

In a rare move, deputy state coroner Anthony Schapel announced the inquest into the crash just four days after the collision, saying it was in the public's interest to start proceedings as soon as possible.

Investigating officer Brevet Sergeant Peter Light told the inquest CCTV showed the truck travelling the final 190 metres of the freeway before the Cross Road intersection in just 4.5 seconds.

Mr Schapel has already recommended all trucks travelling down the freeway from the Crafers exit travel no faster than 60kph.

Transpacific halted its national fleet of 2,800 trucks for a safety audit after Monday's Adelaide crash, but the trucks are now back on the roads.

The grounding of the fleet delayed garbage collection in some parts of Australia.

Freeway speed limits to change

In a swift response to the accident, the South Australian Government has agreed to reduce the freeway speed limit for all trucks between Crafers exit and the toll gate to 60kph from the start of September.

The speed limit had been changed three years ago to 60kph for trucks with five axles or more.

The limit between the slowest vehicle and the fastest vehicle has to be reduced to make sure we have a safe speed environment.

Tony Piccolo

Road Safety Minister Tony Piccolo said all road users would now be limited to a maximum freeway speed of 90 kph on the descent into Adelaide.

He said the maximum speed for light vehicles between the Stirling interchange and the lower arrester bed would be reduced from 100kph to 90kph.

"The limit between the slowest vehicle and the fastest vehicle has to be reduced to make sure we have a safe speed environment," he said.

"To have vehicles driving at too large a gap [in relative speeds] would increase the [accident] risk."

The Government said it was imposing the new restrictions to help calm traffic and would keep working with police, road authorities and the Centre for Automotive Safety Research on effective ways to make the freeway even safer in the longer term.

Motoring organisation the RAA said the speed changes were welcome.

Executive Charles Mountain said drastic action had been needed.

"Reducing the speed limit on the most significant downhill section of the South Eastern Freeway will improve safety for all road users," he said.

Police also announced a road safety blitz for the descent of the South Eastern Freeway to ensure drivers complied with the new speed restrictions.